High Finesse TCFP Resonators on CMOS-Compatible SiN

Silicon nitride has greatly improved the versatility of integrated photonics technologies due to its wide transparency window, compatibility with existing CMOS-foundry infrastruc ture, and its potential for extremely low propagation loss. However, its low refractive index reduces mode confinement, increasing the minimum device footprint of components such as the widely-adopted ring resonator filter, resulting in a height ened need for reduced-bending architecture to maintain high integration density. This work presents CMOS-manufactured transversely-coupled Fabry-P´ erot (TCFP) resonators, a reduced bending substitute for the add-drop ring resonator filter. The cavity mirrors are composed of distributed Bragg reflectors (DBRs), and the resonators exhibit a maximum intrinsic Q of >2 million and a maximum finesse of >400. Device performance is found to be limited by mirror scattering losses, with extracted losses of 1.3-2.2 dB/cm dependent on grating strength.